How much is the kit?
Personally I use a casting urethane called RP-40mod from DascarPlastics. They have a website and also an Ebay store.
It cures with a hardness of D-75 (which is comparable to a bowling ball) and sets up in about 12-15 minutes. You could probably drill it after an hour, but I always wait the full cure time of 24 hours.
I used it when first practicing on plugging balls - it was much cheaper than "real" ball plug. It was also nice that you can buy smaller quantities. I bought the 2 qt kit - didn't think I would ever go through 2 gallons!
I never had any problems with it, but now I prefer the Ebonite clear plug when plugging - longer work time. The rp-40 starts to set up in about 2 1/2 minutes, and when it sets up, it sets up. I've had it set up in mid-pour!
I still use the rp-40 to make my own slugs - drills, cuts, and sands nice and gives a nice smooth finish.
If you can find a Vise exactacator sleeve - Buddies used to sell them for about $10 - it is 1-1/4" inch and perfect for making your own slugs. Before finding that I used a more flexible urethane and made my own molds of thumb slugs (1-1/8 and 1-1/4").
The rp-40 sets up quickly and you can take it out of the mold in about 15 minutes. If you order, make sure you ask for the RP-40mod. The RP-40 dries white/beige and is hard to color. The mod is clear and easier to tint and color match.
You can also find other casting materials that will do what the thumb molding kits do. RTV silicone is a wonderful material for creating custom thumb molds. Don't be afraid to think outside the box.
